Memory arrays include content addressable memory (CAM) used for high performance data search in computers. Most CAM devices utilize static random access memory (SRAM) as data storage devices (utilizing transistors to store information), and additional transistors and complementary transistors for search operations. Often in these CAM devices, search-line access elements and word-line access elements are necessary to operate and program individual memory cells in the memory arrays. These search-line access elements and word-line access elements are often comprised of power intensive, large drive field effect transistors (FET's).
Phase change material can also be utilized to store information for CAM devices. Information is stored in materials that can be manipulated into different phases. Each of these phases exhibits different electrical properties that can be used for storing information.
Chalcogenides are a group of materials commonly utilized as phase change material. They typically contain a chalcogen (Periodic Table Group 16/VIA) and a more electropositive element. Selenium (Se) and tellurium (Te) are the two most common semiconductors in the group used to produce a chalcogenide when creating a phase change memory cell. An example of this is Ge2Sb22Te5 (GST), SbTe, and In2Se3. However, some phase change materials do not utilize chalcogen, such as GeSb. Thus, a variety of materials can be used in a phase change memory cell.
Phase change memory (PCM) technology has lead to increased density enhancements in TCAM/CAM. In search operation, reference match line (ML) timing using resistive-capacitive (RC) sensing schemes is employed to differentiate the search results of “matching”, “non-matching”, and “don't care”. However, RC based sensing schemes are very sensitive to non-idealities, including resistance variability and capacitance mismatch across the match lines.